Urrutienea Dam, France

Introduction

Nivelle River is a 45km long cross-border coastal river. The first 12 km upstream flows into Spain. The next 33 km, including the river’s mouth into the Atlantic Ocean, are in France. This river supports a variety of migratory fish, including 2 species of shad, sea lamprey, European eel, Atlantic salmon and sea trout.

The number of salmon that swim up the river each year has fallen from an average of over 200 fish in 1990-2000 to 100 fish (in some years less than 50) in the last 20 years. This species is, therefore, in sharp decline and particularly threatened in this basin. The causes of the decline are multiple, as in other rivers (habitat quality, water quality, dams, professional fishing, etc.).

This river is also home to the last population of freshwater pearl mussels in the Pyrenees, which live in symbiosis with salmon and trout. It is also in danger of extinction, and great efforts have been made in recent years to save this population. The upstream part of the river is also home to other rare and endangered species, such as the Pyrenean Desman (a small aquatic mammal endemic to the Pyrenees) and the White-clawed Crayfish. Currently, the upstream sector of the river has the best conservation status and spawning grounds for salmon and trout. Unfortunately, this section of the river is inaccessible due to the Urrutienea dam.

Project context and opportunity

Several fish passes have been built on the two main dams in the downstream part of the Nivelle, but the Urrutienea Dam has never been equipped, despite the very high stakes for biodiversity. The owner has always been opposed to the construction of a fish pass. For this reason, the project partners association (with their foundation) purchased the dam in 2022 to remove all the construction and recover a wild river.

This project also has the support of the Government of Navarra in Spain, as it would allow the return of salmon to the Spanish section of the Nivelle. In the context of climate change, the circulation of fish (and of all aquatic organisms in general) is becoming an increasing issue.

In 2022, an initial grant from the Open Rivers Programme enabled technical feasibility studies to be carried out for the Urrutienea Dam. 2023 will be the year of action with the dam removal works.

Project aims

The project’s goals are several :

• restore the alluvial mattress downstream by freeing 6000m3 of pebbles on a deficient section;
• improve the quality of aquatic habitats downstream of the dam for all species (fish, insects, freshwater mussels, etc.);
• allow salmon and trout to access the best spawning areas in the catchment area, which are currently inaccessible;
• improve the quality of aquatic habitats upstream of the dam since the habitats are clogged and homogeneous;
• eliminate the impact on the temperature of the Nivelle. Currently, the dam causes a temperature difference of 2°C in summer.

In the long term, the project partners believe that this project will have a beneficial effect on the salmonid population of the Nivelle, as well as on the very rare and endangered freshwater pearl mussel.

Project achievements

In July 2023, the Federation initiated the project’s initial phase, involving the mid-level threshold (2.5m) levelling. Following this, multiple small floods facilitated the mobilization of sediments upstream in subsequent months (August and September).

The project’s second phase commenced in October 2023, focusing on the complete removal of the threshold down to the bedrock. The outcomes have been notably impressive in terms of hydromorphology:

1. Substantial amounts (thousands of m3) of pebbles and gravel have been released, contributing to the restoration of the alluvial mattress that had been lost over several hundred meters at the dam’s base.
2. Approximately fifteen kilometres of waterways (Nivelle and its tributaries) have been reopened for migrating species, including salmon and eels.

Urrutienea Dam Removal Phase I & II from Fédération Pêche 64 on Vimeo.